1. Field of the Invention
The present invention relates to a toll receiving system, and more particularly to a method for accurately reading information from tickets which has been written at different recording densities.
The present invention relates further to a magnetic recording conversion method for increasing the magnetic recording capacity of a magnetic card type ticket in a toll road system having existing magnetic card type terminal equipment and new equipment which is operable at higher densities than existing terminal equipment.
2. Description of the Related Art
In a long-distance toll road which has several entrance gates and several exit gates at a plurality of locations, a toll amount is collected which depends on the distance driven and the type of vehicle. Specifically, a ticket stores entrance gate information including the type of a car, the date and hour of use, and the entrance gate name. This information is recorded magnetically on a toll road ticket which is distributed to a user at the entrance gate of a toll road. An operator at an exit gate takes the ticket from the user and inserts the ticket into an apparatus which reads information recorded magnetically in the ticket so as to collect the appropriate toll amount.
Furthermore, terminal equipment is provided at entrance gates and exit gates for processing tickets or cards, in some systems called a "Highway Card", which is a prepaid card, and a credit card which is sometimes called a "Separately Paid Plate".
FIG. 9 shows an example of a magnetic card type ticket MC. In FIG. 9, MS denotes a magnetic stripe, on which magnetic recording is made on one side track. In most existing terminal equipment, the recording density is 100 bits per inch (BPI), and the recording system is an FM system. Further, in the terminal equipment at the entrance gate, one track is divided into three areas MS1, MS2 and MS3 along the length of the track for backing up recorded contents, so that the same entrance gate information is recorded in each area. In the terminal equipment at the exit gate, after the entrance gate information has been read, the exit gate information is recorded, including the toll, the exit gate name and the date and hour. The exit gate information and entrance gate information is recorded by overwriting in one of several back-up recording areas. The recorded information is also read to confirm whether recording has been made correctly.
Recently, a trend has developed in which the quantity of information recorded at the exit gate has expanded to accommodate toll collection by credit cards. As a result, the storage capacity for 100 BPI in an existing recording system using only one tract will not be able to accommodate storage of information in the new systems.
Thus, it has become necessary to plan for an increase in the recording capacity, but it is not practical to all at once replace the existing terminal equipment with new equipment at all the gates of a certain toll road because the road must be closed, even if temporarily. Accordingly, the existing terminal equipment is to be gradually replaced with new equipment. In this case, however, tickets having different recording density will be used in a toll road system with existing magnetic card type terminal equipment (hereinafter referred to as "existing equipment") and "new terminal equipment". Accordingly, a method which is able to demodulate magnetically recorded information correctly from tickets of different recording densities is required.
Furthermore, in a conventional magnetic card system, a frequency modulation (FM) system is adopted as a coding system for digital magnetic recording.
FIG. 16 shows an example of a record by an FM system. As illustrated in FIG. 16, an FM system forms an FM code array 402 so as to perform magnetization inversion at boundaries 401A of all the bit cells in a data bit array 400 and at centers 401B of bit cells of respective data bits "1". It is possible to obtain synchronization when reading the information among bits with a magnetization inversion signal 404A at the bit cell boundary Consequently, a high self-synchronizing capacity can be achieved. In FIG. 16, reference numeral 403 denotes a regenerative signal, 404 denotes a detection pulse, 405 denotes a detection clock, 406 denotes a decoder input, 407 denotes decoded data, Tb denotes a bit period, and Tw denotes detection window width.
In the FM system, however, the density ratio (DR) of the maximum bit per inch (BPI) to the maximum flux reversals per inch (FRPI) determined by the characteristics of a magnetic card (DR=BPI/FRPI) and a magnetic head is as low as 0.5. Hence, the FM system is not suitable for high-density magnetic recording.
Further, in a conventional magnetic card system, the width of the detection clock 405 at the read time, corresponding to the detection window width (Tw), is fixed for every system. Therefore, only a magnetic card having a fixed magnetic recording density can be read.